Emission Control Technology to Comply with FTP Revisions 961115
The EPA has proposed revising the Federal Test Procedure (FTP) used to evaluate compliance with emission standards. The revisions involve the addition of two new driving cycles, one of which (US06) includes high speeds and high acceleration rates. EPA has also proposed the operation of the air-conditioner on the “hot stabilized” cycle and the second (SC01) of the two new cycles. In order to meet emission standards on the new procedure, revisions to the emission control technology currently employed in cars and light trucks is required. In this study, we evaluated the range of potential changes to “engine out” emissions required, as well as requirements for catalyst improvements to withstand the higher exhaust temperatures and space velocity.
Analysis of available test data suggested that power enrichment must be very nearly or completely eliminated to meet standards on the US06 test cycle. The combination of stoichiometric operation and US06 driving cycle would lead to an exhaust space velocity increase of 250 percent over current Bag 2 space velocities, and a catalyst temperature increase of 100° to 150° F. The use of air conditioning could lead to NOx increases of 50 to 200 percent, depending on the engine power-to-curb-weight ratio of the tested vehicle.
Control technologies to meet standards on the revised FTP are estimated to include revisions to catalyst size and formulation, as well as calibration changes to engine air fuel ratio set-point, power enrichment and EGR rate. On average, it is estimated that catalyst size would have to increase by 50 percent relative to today's catalysts, and offer significant improvement in thermal durability. Newer catalyst designs, especially those with palladium, appear to offer the capability to withstand the higher temperature exposure.